"It is by his deeds that a lad distinguishes himself if his conduct is pure and right"
Solomon brings up just the right issues. For young people, they want to know how they will make their mark in the world. How can they be noticed? The answer is what you do, not your boasts or dreams or potential. It is by what you actually do.
This is the Hebrew word maalal which means deed or practice. It has to do with action and work that the person performs.
This is the Hebrew word naar which is the word boy, youth, a person in their early life. Before you have really done anything, it is not your boasts or dreams that are impressive to others and what will set you apart. It is the things that you do. Too many young people are trying to impress people with their dreams or their skills instead of by the things that they actually do. Now it is true that the deeds that these young people do will often be mundane rather than heroic, but it is still their actions that make them stand out.
There is also another angle on this and that is that Solomon is saying that great dreams are wonderful, but as you live your life you must actually do something. It is the actual deeds that you do over your life that will distinguish yourself.
This is the Hebrew word nakar which means recognize, know, respect. If a young person wants to separate themselves from the rest, they will do this by what they do.
if his conduct is pure and right
There is a huge if-then clause in this verse. It appears in the second half of the verse. If you want to build respect for yourself and make a name for yourself, then do positive things. But they must be done within the box of the Ten Commandments. What is pure and right? Don't do good things after you have dipped into the pool of selfish wickedness and then throw little gifts around.
There will be temptation for young people to try and make their mark or gain respect through sin, pride, selfishness, wickedness, disrespect, etc. All of these will bring a certain level of notoriety immediately but will destroy the potential of your life. Resist the temptation to be a somebody this way.